Laminated safety glass



United States Patent 3,271,233 LAMHNATED SAFETY GLASS Edward Lavin,Longrneadow, and George E. Mont, Springfield, Mass, assignors toMonsanto Company, St. Louis, Mo, a corporation of Delaware No Drawing.Filed Sept. 21, 1965, Ser. No. 489,038 19 Claims. (Cl. 161-199) Thisinvention relates to improved laminated safetyglass. More particularly,this invention relates to laminated safety-glass having an interlayer ofa plasticized polyvinyl acetal, which has higher resistance topenetration.

Laminated safety-glass comprises two or more glass panels bound with aninterlayer of a transparent, adherent plastic. The usual plasticinterlayer is a plasticized polyvinyl acetal resin formed in a sheet orfilm with a thickness of about 0.015 inch or more. The major commercialuse of these safety-glass compositions is for automobile Windshields, aswell as for Windshields in other moving vehicles. The ever increasingnumber of automobiles and the faster speed of travel today coupled withthe greater area of modern day Windshields has accentuated the need forimproved laminated safety-glass. These structures must not only helpprotect per-sons in a car from being struck by flying objects from theoutside but should prevent occupants from penetrating the Windshield onimpact after a sudden stop. The danger of being cut by glass in thewindshield can occur not only when a body strikes the windshield andpenetrates it but also when the windshield is broken and glass fragments:are released. The interlayer therefore benefits the struc ture not onlyby adhering to the glass particles but also has the added advantage ofabsorbing energy on impact thereby decreasing the possibility of skullfracture which may occur when a head strikes the windshield, while alsosupplying added resistance to penetration.

The interlayers in present day commercial Windshields usually containabout 0.2 to 0.8% moisture. It has been reported that some increase inresistance to penetration is found if the moisture content of theplastic interlayer is considerably higher. However, the presence ofincreased moisture alone to improve the penetration resistancesufficiently is impractical because the clarity of the windshield isadversely afiected by the formation of bubbles between the interlayerand the glass or within the interlayer. Further, the presence of excessmoisture may cause delamination. Consequently, the automotive andlaminating industries have not been able to take significant advantageof this method of improving resistance to penetration.

The principal object of this invention is to provide laminatedsafety-glass having improved safety features.

A further object of this invention is to provide a laminatedsafety-glass having improved resistance to penetration by impactingobjects such as the human head.

A particular object of this invention is to provide improved physicalproperties in laminated safety-glass.

Another object of this invention is to provide methods and means toaccomplish the preceding objects.

These and other objects are accomplished in a laminated safety-glass bybonding two glass panels with an interlayer of a plasticized polyvinylacetal resin; said interlayer having a moisture content of 0.2 to 0.8%by Weight and containing suflicient metal salts of substituted aceticacids wherein the substituted acetic acid portion is selected from thegroup consisting of glycine, glycolic acid, phenylacetic acid,chloroacetic acid and phenoxymethyl acetic acid, to produce analkalinity titer of at least 3 wherein said metal is selected from thegroup consisting of alkali and alkaline earth metals.

The alkalinity titer is the number of milliliters of 0.01

3,27l,233 Patented Sept. 6, 1966 normal hydrochloric acid required toneutralize grams of the polyvinyl acetal resin. This is an arbitrarystandard used to designate the alkalinity of the resin. The alkalinitytiter is usually determined prior to plasticization by dissolving 7grams of the polyvinyl acetal resin in 250 cc. of preneutralized ethylalcohol and titrating with 0.005 normal hydrochloric acid to theendpoint using brom-phenol blue indicator and calculating from theresult obtained to determine the milliliters of 0.01 normal acidrequired for 100 grams resin.

It is customary to stabilize polyvinyl acetals for interlayers withpotassium or sodium hydroxide and/or potassium or sodium acetate byadding small amounts of these materials. These are normally added duringthe preparation of the polyvinyl acetal. However, these materialsincrease the titer level without improving the penetration resistance orimpact strength of the laminate except at objectionably high titerlevels. Moreover, large amounts of these salts or bases tend to increasethe color of the extruded plasticized resin which is undesirable in aninterlayer. The presence of such alkaline materials produces thealkalinity titer in conventional polyvinyl acetal interl-ayers.

The following examples are given in illustration of the invention andare not intended as limitations thereof. All parts and percentages areby weight unless otherwise specified.

Example I is set forth as a control to illustrate the poorer resultsobtained when using potassium acetate to control the titer.

Example I (a) This example uses a conventional polyvinyl acetalinterlayer for safety-glass. It is a polyvinyl butyral containing 18.8%vinyl alcohol by weight and having an alkalinity titer of 20. This titeris due to the presence of potassuim acetate (K acetate) in the polyvinylbutyral. The resin is plasticized with 44 parts, per hundred parts ofresin, triethylene glycol di(2-ethyl butyrate) and has a moisturecontent of about 0.4%. The interlayer is formed into sheets 0.015 inchthick (15 gauge) and 0.030 inch thick (30 gauge). These interlayersheets are used as controls.

Sets of ten lglass laminates are individually prepared by interposingthe 15 gauge interlayer between two 24 x 36 x 0.125 inch panels of glassand the 30 gauge interlayer between two 12 x 12 x 0.125 inch panels ofglass. The resulting laminates are then subjected to a temperature ofabout 275 F. at a pressure of p.s.i. for approximately 10 minutes tobond the laminate or panels together.

Further sets of glass laminates are similarly prepared as above usingplasticized polyvinyl butyral containing potassium acetate at varyinglevels producing the following alkalinity titers:

The laminates prepared by the above procedure are then subjected to meanbreak height tests according to the recently established tentativespecifications set up by the Society of Automotive Engineers, theSubcommittee on Automotive Glazing and the results tabulated in Table I.

In essence, the mean break height test comprises placing the laminate ina horizontal position with a frame or edge support and while maintaininga constant laminate temperature, which is 70 F. in this series, allowinga 22 pound spherical ball (referred to as a head form) to drop from adesignated height against approximately the middle of the laminate madewith the 15 gauge interlayer. This testis repeated at increasingball-drop heights to determine the approximate height in feet at which50% of the laminates tested will resist penetration. In other Words, themean break height of a laminate is a measure of the ability of thatlaminate to absorb the energy of an impacting object. The same test isused with the laminates made with 30 gauge interlayer except that apound steel ball is used on the smaller laminate.

l vent windshield penetration by any part of the human body uponcollision at todays rates of speed. As a result of this invention,windshield laminates can be prepared which from test results indicatethat the laminates would 5 not be penetrated on collision impacts evenwhere the Results of the mean break height test for the laminatesautomobile was travelling at speeds in excess of 25 mph. of Example Iare tabulated in Table 1. Unless otherwise In other words, at normalinterlayer moisture contents, specified, the values for mean breakheights in the disif the alkalinity level is controlled in accordancewith the cussion refer to those for laminates using 30 gaugeinterpractice of this invention, a far superior safety laminate layers.will result.

TABLE I As earlier noted, the moisture content of the polyvinyl[Examples 1mm butyral interlayer cannot be increased too greatly ifbubble problems are to be avoided. In addition, the mois- Mean Breakture content of the interlayer is rather difficult to control AlkalinityHeight (Fm) Percent since it can be alfected by atmospheric conditionsand the Example Titer, cc. lgoistturte particular laminating process.Consequently, it is pre- 15 gaugei 3O gaugei on ferred that the moisturecontent be maintained rather low, i.e., 0.2 to 0.8%. On the other hand,the alkalinity titer K Acetate: of the polyvinyl butyral interlayer canbe readily increased 1 g3 8&8 by the addition of these salts ofsubstituted acetic acids 42 9 5 43 during the preparation of thepolyvinyl butyral resin. The

minimum quantity of salts of substituted acetic acid necl'lhick essofintenayen essary to effect a particular improvement in penetrationExamples II-VI are set forth to illustrate the impact iesistance ofthe.fina1.'1aminate has been found to be strength of glass laminatesprepared from polyvinyl mvgsely proportpnal m degree to pref.erredbutyral interlayers wherein the titer is due solely to salts molsmrecontent greater Impact stiength 1S achleved of substituted acetic acid.These examples are prepared at the upper of to (18% molsuirelranga Theand tested according to the procedure of Example I. The 22 83 1 5 t gsgzfg i gf ggg fgg 0 I data on Examples II VI are tabulated m TableTable III illustrates the small effect of moisture within TABLE II thenormal moisture range in the absence of any salts on [Examples ILVH theimpact strength of various sets of glass laminates. The plasticizedinterlayer sheets having an alkalinity titer Moan Break of zero areprepared from a resin thoroughly Washed after Example Salt Titer s H gsgswelling in alcohol-water as described below.

15 30 TABLE III.EFFECT OF MOISTURE ON MEAN BREAK gauge gauge HEIGHTPotassium phenyl acetate- 33 3. 4 13. 7 0.35 Mean Break Height Potassiumphenoxy- 24 3.0 12.6 0. Percent (Feet) methyl acetate. Alkalinity TiterMoisture Lithium glyeolate 23 2.8 12.2 0.41 Content Magnesium glycolate15 2.9 12. 3 0. 43 15 gauge 30 gauge Potassium chloroaeetate 6 3.6 13.90.46 Interlayer interlayer .06 2.3 7.5 The control samples show resultsobtained using potas- .31 2.4 7.7 sium acetic alone at titers from 20 to42. The substig'g g-g tuted acetic acid salts show mean break heightsthat are I75 3:0 8:3

significantly better than those obtained with potassium acetate attiters from 15 to 33.

A comparison of Examples I(a)I(c) With Examples II-VI show that theimpact resistance is nearly doubled when using substituted acetic acidsalts rather than potassium acetate to control titer. This issignificant in that high potassium acetate titers tend to causediscoloration in glass laminates.

The substituted acetic acid salts used in the practice of this inventionare the alkali and alkaline earth metal salts of glycine, glycolic acid,phenylacetic acid, chloroacetic and phenoxymethyl acetic acid. i

The laminated safety-glass of this invention is especially etficient inthat the improved resistance to penetration is balanced over a widetemperature range. The impact tests shown in the examples are conductedat as low as 4 F. and as high as 120 F. indicate that these laminatesexhibit improved properties over a wide temperature range.

It is well known that an increase in the thickness of the plasticizedpolyvinyl butyral interlayer Will give some improvement to thepenetration resistance of the laminates. This invention is equallyapplicable to the thicker laminates. In fact the use of an 0.030 inchinterlayer containing salts of these substituted acetic acid results inmean break heights more than double those of the 0.015 inch interlayersof the examples. One of the prime goals of the safety councils for safermotor vehicles is to pre- Taken alone the presence of from. 0.1 to 0.8%water in the interlayer has ilttle etfect on the mean break height.However, this effect is increased in the presence of the salts of thisinvention. The result is that laminates containing the salts ofsubstituted acetic acids and having a moisture content in the upper endof the 0.2 to 0.8% range would have somewhat better impact resistancethan those in the lower end of the moisture range.

In order to avoid alkali burns on processing of the resin duringplasticization or extrusion and to avoid excessive sensitivity tomoisture in the interlayers which may result in edge separation of thelaminates it is highly preferred to limit the alkalinity titer so thatit is not over 100. For the above reasons, it is a preferred embodimentof this invention to limit the alkalinity titer to a maximum of 60within the range of 0.2 to 0.8% moisture content. The lower limit ofeffectiveness of the alkalinity titer for improved impact strength isabout 3. Within a moisture content of 0.2 to 0.8%, a preferred range ofalkalinity titer is 3 to 40.

In general, the laminates are prepared by interposing the plasticizedpolyvinyl butyral interlayer between a pair of glass plates and thensubjecting the resulting assembly to a temperature of 190 to 325 F. anda pressure of to 225 psi. for at least '10 minutes to bond the assemblytogether.

The polyvinyl acetal resins which are employed in the present inventionmay be made from various unsubstituted ketones containing an activecarbonyl group or from mixtures of unsubstituted aldehydes and ketones.Thus, formaldehyde, acetaldehyde, propionaldehy-de, butyraldehyde,valeraldehyde, hexaldehyde, benzaldehyde, crotonaldehyde, cyclohexanoneand the like and mixtures thereof may be utilized. In general, theacetal resin is made by reacting an aldehyde with hydrolyzed polyvinylester where-in the canboxylic moiety is derived from an aliphatic acidof from 1 to 8 carbon atoms such as for-mate, acetate, propionate,butyrate, Z-ethylhexylate, etc. in the presence of a solvent ior theproduct and precipitating the resin product with water. Alternatemethods might include carrying out the reaction in the presence of anonsolvent dispersing medium such as water or a non-solvent mixture ofwater and solvent, e.g., a water-ethanol mixture. More detailed methodst'or preparing such resins are set 'forth in Morrison et al. US. PatentRe. 20,430, dated June .29, 1937, and Lavin et al. U.S. Patent No.2,496,480. In general, polyvinyl acetal resins made from saturatedlolwer unsubstituted aliphatic aldehydes are the most suitable. Thesewould include polyvinyl acetal resins made from unsubstituted saturatedaliphatic alde'hydes containing less than 6 carbon atoms such aspropionaldehyde, valeraldehyde and especially those made fromformaldehyde, acetaldehyde, butyraldehyde and mixtures thereof.Particularly preferred are polyvinyl acetal resins made frombutyraldehyde.

:In general the polyvinyl acetal resins employed have Staudingermolecular Weights ranging from about 50,000 to 600,000 and preferablyfrom 150,000 to 270,000 and may be considered to be made up, on a weightbasis, of from 5 to 25% hydroxyl groups, calculated as polyvinylalcohol, to 40% ester, and preferably acetate groups, calculated aspolyvinyl ester, e.g., acetate, and the balance substantially acetal.When the acetal is butyraldehyde acetal, the polyvinyl acetal resin willpreferably contain, on a weight basis, from 9 to 30% hydroxyl groups,calculated as polyvinyl alcohol and from 0 to 3% ester, e.g., acetate,groups, calculated as polyvinyl ester, the balance being substantiallybutyraldehyde acetal.

The resin prepared according to the above methods will containapproximately 10-40 cc. alkalinity titer which is generally composed ofpotassium acetate or sodium acetate depending on the process used. Inorder to replace these salts with the salts of this invention, the resinis swelled in a mixture of alcohol-water (0.960 sp. gr.) at about 40 C.for about 1 hour and then washed thoroughly with water until the driedresin is neutral to bromphenol blue in the alkalinity titer test.Appropriate amounts of the salts of this invention are then added to aslurry of the washed zero alkalinity titer resin parts water per part ofresin). After thirty minutes the grains are filtered and dried. Uniformdistribution of the salts is further effected by the plasticizationstep.

An alternative method of adding the salts to a zero titer resin is byadding it with the plasticizer during the plasticiz-ation step.

The resin produced may be plasticized to the extent of about 20 to 80parts plasticizer per 100 parts resin and more commonly between 40 and50 parts for norm-a1 windshield use. This latter concentration isgenerally used with polyvinyl butyrals containing 18 to 23% vinylalcohol by Weight. In general, the plasticizers which are commonlyemployed are esters of a polybasic acid or a polyhydric alcohol.Particularly suitable are triethylene glycol di(2-ethyl butyrate),dibutyl sebacate, and di- (betabutoxyethyl)adipate. The resultingplasticized resin mixture is then generally extruded in the form ofsheets and cut to size to produce the interlayers used in the presentinvention. The plasticized polyvinyl butyral resin interlayer isself-adhesive in nature thereby eliminat- 6 ing the need for a separateadhesive to bond the glass laminate together.

Safety-glass laminates find special application in the automotive andaircraft industries for protecting passengers both against the hazardsof flying objects and to reduce injury caused by bodily impact againstthe laminate. Wherever else glass or transparent panels are utilizedsuch as in the building trade, the protection atforded by safety-glasshas become increasingly important. The laminates of the presentinvention increase the advantages of utilizing safety-glass because oftheir improved safety performance.

It is obvious that many variations may be made in the products andprocesses set forth above Without departing from the spirit and scope ofthis invention.

What is claimed is:

1. An improved interlayer for laminated safety glass comprising aplasticized polyvinyl acetal resin; said interlayer having a moisturecontent of 0.2 to 0.8% and containing sufficient alkali and alkalineearth metal salts of substituted acetic acids wherein the substitutedacetic acid portion is selected from the group consisting of glycine,glycolic acid, phenylacetic acid, chloroacetic acid and phenoxymethylacetic acid to produce an alkalinity titer of at least 3.

2. An improved interlayer as in claim 1 wherein the polyvinyl acetal ispolyvinyl butyral.

3. An improved interlayer as in claim 2 wherein the polyvinyl butyralhas a vinyl alcohol content of 9 to 30% by weight and is plasticizedwith from 20 to 50 parts plasticizer per parts polyvinyl butyral.

4. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is potassium glycinate.

5. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is magnesium glycolate.

6. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is lithium glycolate.

7. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is lithium phenyl acetate.

8. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is lithium phenoxymethyl acetate.

9. An improved interlayer as in claim 2 wherein the substituted aceticacid salt is potassium chloroacetate.

10. An improved laminated safety-glass comprising two layers of glassbonded to a plasticized polyvinyl acetal interlayer; said interlayerhaving a moisture content oi 0.2 to 0.8% by weight and containingsuflicient alkali and alkaline earth metal salts of substituted aceticacids .Wherein the substituted acetic acid portion is selected from thegroup consisting of glycine, glycolic acid, phenylace-tic acid,chloroacetic acid and phenoxymet'hyl acetic acid to produce analkalinity titer of at least 3.

11. An improved laminated safety-glass as in claim 10 wherein thepolyvinyl acetal is polyvinyl butyral.

12. An improved laminated safety-glass as in claim 11 wherein thepolyvinyl butyra-l is plasticized with from 20 to 5 0 parts plasticizerper 100 parts polyvinyl butyral.

13. An improved laminated safety-glass as in claim 11 wherein thesubstituted acetic acid salt is potassium glycinate.

14. An improved laminated safety-glass as in claim 11 wherein thesubstituted acetic acid salt is magnesium glycolate.

15. An improved laminated safety-glass as in claim 11 wherein thesubstituted acetic acid salt is lithium glycolate.

16. An improved laminated safety-glass as in claim 11 wherein thesubstituted acetic acid salt is lithium phenyl acetate.

17. An improved laminated safety-glass as in claim 11 wherein thesubstituted acetic acid salt is lithium phenoxymethyl acetate.

13. An improved laminated safety-glass as in claim d 11 wherein thesubstituted acetic acid salt is potassium chloroacetate.

19. The method of preparing an improved plasticized polyvinyl acetalinterlayer which comprises swelling a polyvinyl aceta-l resin in amixture of alcohol and water at about 40 C. for about 1 hour and washingwith water until the resin has a zero alkalinity titer, then adding toan aqueous slurry of the resin sufficient alkali and alkaline earthmetal salts of substituted acetic acids wherein the substituted aceticacid pontion is selected from the group consisting of glycine, glycolicacid, phenylacetic acid, chloroacetic acid and phenoxymethyl acetic acidto produce an alkalinity titer of at least 3, adjusting the moisturecontent of the polyvinyl acetal to 0.2 to 0.8% by weight,

C) 0 plasticizing the polyvinyl acetal, and forming the interlayer.

Retierences Cited by the Examiner UNITED STATES PATENTS 2,456,46212/1948 StaInatOff 260-73 2,496,480 2/1950 Lavin et a1. 26073 2,946,7117/1960 Bragaw et a1. l61-l99 3,231,461 1/1966 Mattimoe 161199 FOREIGNPATENTS 136,461 3/1950 Australia.

ALEXANDER WYMAN, Primary Examiner.

W. J. VAN BALEN, Assistant Examiner.

10. AN IMPROVED LAMINATED SAFETY-GLASS COMPRISING TWO LAYERS OF GLASSBONDED TO A PLASTICIZED POLYVINYL ACETAL INTERLAYER; SAID INTERLAYERHAVING A MOISTURE CONTENT OF 0.2 TO 0.8% BY WEIGHT AND CONTAININGSUFFICIENT ALKALI AND ALKALINE EARTH METAL SALTS OF SUBSTITUTED ACETICACIDS WHEREIN THE SUBSTITUTED ACETIC ACID PORTION IS SELECTED FROM THEGROUP CONSISTING OF GLYCINE, GLYCOLIC ACID, PHENYLACETIC ACID,CHLOROACETIC ACID AND PHENOXYMETHYL ACETIC ACID TO PRODUCE AN ALKALINITYTTITER OF AT LEAST 3.